A large spectrum of avian influenza virus to which the human population is naTve is present in wild aquatic birds, and highly pathogenic H5N1 avian strains are currently circulating in several countries in southeast Asia where they have caused dozens of human fatalities. These strains are of particular concern because they are resistant to the most cost-effective antiviral drugs, amantadine and rimantadine. The emergence of a novel transmissible influenza virus against which the population has little or no immunity would cause a global pandemic, for which no vaccine is available. Current influenza vaccines are produced from viruses that are adapted to grow well in embryonated hens' eggs, whereas highly pathogenic avian influenza viruses are lethal for hens' eggs, making the current methods of vaccine production problematic. Alternative approaches to develop effective influenza vaccines are therefore urgently needed. In an effort to develop alternatives for influenza vaccine production and in response to a pandemic threat, our goal in this project is to determine whether influenza virus-like particle based vaccines will provide protective immunity against a highly pathogenic avian influenza virus. Additional goals are to address other shortcomings of current influenza vaccines: they exhibit limited efficacy, they fail to protect against infection at mucosal surfaces, and the observed immunity is highly strain-specific and of short duration. Thus, we will develop approaches to enhance the immunogenicity of influenza vaccines, to enhance memory responses to the vaccine, and to induce effective immune responses at mucosal surfaces which may be protective against a broader range of viral strains. In addition to a panel of assays to monitor humoral and cellular immune responses, we will make use of novel transgenic mice which have been constructed to directly measure the magnitude of B cell memory generated in response to immunization. The specific aims of the project are:1. to produce virus-like particles (VLPs) incorporating influenza viral glycoproteins and matrix (M1) protein; 2. to characterize humoral and cellular immune responses after immunization with influenza VLPs and their protective efficacy; and 3. to develop more effective influenza VLP-based vaccines by incorporation of ligands designed to target the VLPs to antigen-presenting cells.